Remoção de contaminantes e hidrodinâmica em sistemas alagados construídos contendo chicanas dispostas de diferentes formas

Abstract

This study aimed to evaluate the performance of three Horizontal Subsurface Constructed Wetlands (HSS-CW) with different baffle arrangements and cultivated with Pennisetum setaceum in the removal of pollutants, including microcontaminants, from wastewater produced at a university. Furthermore, it also aimed at evaluating the productivity and extraction capacity of the used plant species, and the hydrodynamic behavior in the different systems. Three fiberglass (SACs-EHSS) were used: SAC A, built without baffles, SAC B, with baffles fixed on the sides and SAC C, with baffles above and below the bed. The experiment was conducted for nine months, treating the effluent of a university campus, in three phases. For the evaluation of the microcontaminant removal, some pharmaceuticals and endocrine disrupters were selected: ibuprofen (IBU), acetaminophen (ACE), 4-octylphenol (4OC), caffeine (CAF), 4-nonylphenol (4NP), naproxen (NPX), bisphenol-a (BPA), diclofenac (DCF), estrone (E1), estradiol (E2), ethinyl estradiol (EE2) and estriol (E3). Among the twelve evaluated microcontaminants, the endocrine disrupters 4-NP and EE2 were not identified in any of the samples. The influent concentrations in the three phases ranged from 87.3 to 2559.2 ng L-1 for pharmaceuticals, 584.6 to 1658.3 ng L-1 for caffeine, and 49.1 to 584 ng L-1 for endocrine disruptors. All three constructed wetlands with different baffle arrangements were efficient in removing the evaluated organic pollutants. The experiment was conducted in three phases, and it was verified that the organic loading rate (OLR) in phase II were significantly higher (p <0.05) than the OLR in phases I and III. The removal efficiencies of COD were significantly higher in phase III for all SACs, with values equals to 74%, 75% and 74% for SACs A, B and C, respectively. The treatment SACs-EHSS showed good removal efficiencies of COD, TS, TVS, TFS, TP, TN, NO2- and NO3-. No significant difference was found between the baffle and non-baffle systems (p>0.05). The productivity and nutrient extraction capacity of the grass were also satisfactory. The study showed that flooded systems have functions beyond the promotion of effluent treatment, such as improving the aesthetics of the environment with the good productivity of ornamental species. Two hydrodynamic tests were performed at the beginning and after 8 months of operation, using a saline tracer (NaCl). Sampling and determination of electrical conductivity (EC) were performed every 15 minutes. As a result, there was greater longitudinal dispersion of the fluid and degree of mixing in units A and B and lower in C for both tests. Thus, it is observed that there is an effect of the use of baffles in the reactor hydrodynamics. However, the horizontal baffle dimensions might have caused an increase in liquid flow rate, leading to greater liquid dispersion and reduced hydraulic residence time.